Strategy for fueling a diesel engine

Abstract

A compression ignition engine ( 10 ) operates to fuel an engine cylinder ( 12 ) to create an in-cylinder air-fuel charge and to cause that charge to autoignite. A fuel injector ( 20 ) operates to inject fuel into the engine cylinder for substantially the entire duration of a first phase ( 24 ) of fuel injection at substantially the maximum injection pressure that the fuel injector can deliver to create a premixed fraction of the in-cylinder air-fuel charge prior to autoignition. As the first phase ends, fuel injection transitions to a second phase ( 26 ) which commences in advance of autoignition. During the second phase, the fuel injector injects fuel into the engine cylinder at a rate of injection that is significantly less than the rate of injection used during the first phase.

What is claimed is: 
     
       1. A method of operating a compression ignition engine by fueling an engine cylinder to create an in-cylinder air-fuel charge and to cause that charge to autoignite, the method comprising:
 operating a fuel injector to inject fuel into the engine cylinder for the entire duration of a first phase of fuel injection at a maximum injection pressure that the fuel injector can deliver to create a premixed fraction of the in-cylinder air-fuel charge prior to autoignition, with the duration of the first phase of fuel injection being based at least in part on a speed and a load of the engine; 
 operating the fuel injector to inject a second phase of the same fuel into the engine cylinder at an injection pressure less than the maximum injection pressure that the fuel injector can deliver, with the second phase of fuel being injected in advance of autoignition of the first phase of fuel and the injection pressure of the second phase of fuel injection being based at least in part on the speed and load of the engine. 
 
     
     
       2. The method set forth in  claim 1  in which using a sensor to provide data representing a crank angle at which autoignition is expected to occur comprises processing data representing the crank angle at which autoignition occurred during an immediately preceding engine cycle. 
     
     
       3. The method set forth in  claim 1  in which the second phase of fuel injection comprises operating the fuel injector to inject fuel into the engine cylinder at an injection pressure less than the maximum injection pressure that the fuel injector can deliver for the entire duration of the second phase of fuel injection. 
     
     
       4. The method set forth in  claim 1  comprising controlling at least one variable characteristic of at least one of the first and second phases of fuel injection as a function of engine speed and engine load. 
     
     
       5. The method set forth in  claim 4  in which controlling at least one variable characteristic of at least one of the first and second phases of fuel injection as a function of engine speed and engine load comprises controlling a crank angle at which the first phase of fuel injection commences to within a window that extends from 30° before TDC to 10° deg after TDC. 
     
     
       6. The method set forth in  claim 5  in which the fuel injector is operated to inject fuel into the engine cylinder for the entire duration of the first phase of fuel injection at an injection pressure of at least of 3,000 bar.